Industrial robots, which are capable of gripping an object with a robot hand and carrying the object from one position to another position or exchanging works by mounting a work on and removing the same from the chuck of a machine tool, have come into use. The general construction of such an industrial robot includes a robot body capable of turning and moving vertically with respect to the stationary base of the industrial robot, a robot arm laterally extendable with respect to the robot body, and a wrist unit joined to the free end of the robot arm for turning and swinging motion. A robot hand is joined to the wrist unit. Since an industrial robot consists of such operating components, facilitating the manufacturing processes for each operating component through simplifying the construction results in a reduction of the total cost of the industrial robot. Accordingly, efforts are being made to develop improvements for simplifying the construction as well as for improving the performance of those operating components along with the increasingly widespread use of industrial robots.